Volume controller

ABSTRACT

A volume controller for controlling the voltage of at least one signal transmitted in a signal path in matching with the characteristic impedance of the signal path, where the signal is branched to two differential outputs by a branch circuit comprising a bridge circuit of four resistance-arms to amplify the difference between the two differential outputs in a difference amplifier which has a feedback circuit comprising a variable resistor connected between the output of the difference amplifier and one of two inputs of the difference amplifier. The voltage of the output of the difference amplifier can be controlled within an extremely wide level range in response to control of the control means which gangs the variable resistor of the feedback circuit and variable one of the four resistor-arms of the bridge circuit.

United States Patent [72] inventors Shigeru Niki;

Taltanobu llashimoto; Michio Yoshiolra, all oi Tokyo-to, Japan [21]Appl. No. 772,660 [22] Filed Nov. 1, 1968 [4S] Patented July 27, 1971[73] Assignee Koltusai Denki Kabushiki Kaisha Tokyo-to, Japan [32]Priority J ly 9, 1968 33] Japan [31 43/47512 [54] VOLUME CONTROLLER 3Claims, 7 Drawing Figs.

[521 (LS. Cl 330/59, 330/103, 330/69, 330/146, 330/185 [51] Int. Cl..H03l 17/00, 1103f 1/36 [50] Field of Search 330/59 [56] ReferencesCited UNITED STATES PATENTS 3,258,707 6/1966 Lawrence, Jr 330/593,260,945 7/1966 Kalmus et a1. 330/59 X 3,436,671 4/1969 Fenton et a1330/59 X Primary Examiner-Nathan Kaufman AttorneysRobert E. Burns andEmmanuel J. Lobato ABSTRACT: A volume controller for controlling thevoltage of at least one signal transmitted in a signal path in matchingwith the characteristic impedance of the signal path, where the signalis branched to two differential outputs by a branch circuit comprising abridge circuit of four resistance-arms to amplify the difference betweenthe two dilTerential outputs in a difference amplifier which has afeedback circuit comprising a variable resistor connected between theoutput of the difference amplifier and one of two inputs of thedifierence amplifier. The voltage of the output of the differenceamplifier can be controlled within an extremely wide level range inresponse to control of the control means which gangs the variableresistor of the feedback circuit and variable one of the fourresistor-arms of the bridge circuit.

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VOLUME CONTROLLER change of signal-level, and mismatching with thecharacteristic impedance of the transmission line. Moreover, theconventional volume controller is usually unsuitable to beremote-controlled by an external signal or signals.

An object of this invention is to provide volume controllerseliminatable of the above mentioned disadvantages and having anextremely wide control range.

Another object of this invention is to provide a volume control unit ofa fader suitable to be remote-controlled by an external control voltage.

The principle of this invention will be better understood from thefollowing more detailed discussion taken in conjunction with theaccompanying drawings, in which the same or equivalent parts aredesignated by the same reference numerals, characters and symbols, andin which:

FIG. 1 is a block diagram for describing the principle of thisinvention;

FIG. 2 is a circuit diagram for illustrating an embodiment of thisinvention;

FIG. 3 illustrates a characteristic curve for describing the operationcharacteristic of the embodiment shown in FIG. 2;

FIG. 4 is a circuit diagram for illustrating another embodiment of thisinvention;

FIGS. SA and 5B illustrate characteristic curves for describing theoperation characteristic of the embodiment shown in FIG. 4; and

FIG. 6 is a circuit diagram for illustrating another embodiment of thisinvention.

With reference to FIG. 1, the principle of this invention will first bedescribed. A matching circuit 2 matches with the line impedance withinthe range of all operation frequencies. An input signal 5, applied froman input terminal 1 passes through the matching circuit 2 and is appliedto a branch circuit 3, which produces two branched outputs S, and 8,.These two outputs S, and S, are respectively applied to two inputs of adifference amplifier 4. The output of this difference amplifier 4 is fedback to one of the two inputs of the difference amplifier 4 through afeedback circuit 5. An output signal S, is derived from an outputterminal 6 connected to the output of the difference amplifier 4.Details of the construction and operation of this volume controller willbe understood from the following description of embodiments of thisinvention.

FIG. 2 shows an embodiment of the volume controller of this inventionhaving the above-mentioned construction. In FIG. 2, a resistor R, is amatching resistor, and a resistor R is a coupling resistor. The branchcircuit 3 is composed of a bridge circuit having four resistor-arms(resistors R R, and R, and a variable resistor R and if two pair ofopposed terminals (P,, P,) AND P P The signal S, is applied, through theresistor R to one pair of opposed terminals I and P,, and two outputs Sand S, branched at the other of opposed terminals (P P are respectivelyapplied to a minus input terminal I of the difference amplifier 4 and aplus input terminal I, thereof. A resistor 8 is a matching resistor ofoutput side. A variable resistor R, is a feedback resistor and gangswith the variable resistor R In the above-mentioned construction, if thedifference amplifier 4 has a gain G with respect to the input signal Sof the minus terminal 1,, the input impedance Zi of the differenceamplifier 4 at the minus terminal I, can be indicated as follows:

where reference r and r are respectively resistances of the resistors Rand R Therefore, the equilibrium condition of the bridge circuit 3 canbe indicated as follows:

where references r, and r, are respectively resistances of the resistorsR and R while the term r //Z, indicates a resultant resistance ofparallel-connected resistors r and Z If each of the resistors R and R isa variable resistor of resistance 500 kilo-ohms, and the bridge circuit3 balances when the variable resistor R, has the value of 500 ohms, thenthe equation (2) is as follows, where resistances r and r have therespective values of 40 kilo-ohms and 3 kilo-ohms:

Therefore, the resistance r, of the resistor R, becomes a value 29.4kilo-ohms.

Moreover, the'equilibrium condition of the bridge circuit 3 can beindicated as follows by use of the resistances r r r r and r, from theequation (2):

If respective input voltages of the minus and plus terminals I and I, ofthe difference amplifier 4 are assumed as voltages E and 5,respectively, since influences from relatively high resistances R R andR are negligible, the output voltage E of the difference amplifier 4 canbe indicated as follows:

+1 dE -E E a 2 i1 Where dE, indicates a difference between the voltagesE and 15, In this case, since the resistance r,, of the resistor R isconstant, the output voltage E, can be indicated by a function of theresistance r, of the resistor R and the input voltages E and E Moreover,if the bridge circuit 3 is balanced so that the voltages E and E areequal to each other, the output voltage E, becomes zero and theattenuation in the volume controller of this invention becomes maximum.The output voltage E is adjustable to a desired value in accordance withchange of the resistance r-, of the resistor R and of the voltages E and8,

FIG. 3 shows an attenuation characteristic of the embodiment shown inFIG. 2 in case where the variable resistors R and R have the samechange-characteristic of resistance and the maximum resistance 500kilo-ohms. The maximum a.- tenuation A of this characteristic exceedsdb. (decibels). Accordingly, it is understood that the attenuation ratioof the output voltage E to the input signal S, applied from the inputterminal 1 can be changed within an extremely wide changing range inaccordance with change of the resistance of a gang resistor comprisingthe variable resistors R and R FIG. 4 shows another embodiment of thisinvention in which attenuation ratio of an output voltage E, to avoltage of input signal S, can be changed by an external control voltageV, applied across a pair of control terminals 10a and 10b. In thisembodiment, the variable resistor R is composed of a photoconductivecell whose resistance varies with the illumination on the cell, and theresistor R is composed of a resistor R and a photoconductive cell Rwhich are connected in parallel with each other. Such photoconductivecell can be formed by use of cadmium sulfide (CdS) wafer. Thephotoconductive cells R and R are respectively illuminated by smallelectric lamps L and L, which are excited by an external control voltageV,. supplied, as a manipulated variable,

across the terminals a and 10b. The photoconductive cell R and the smallelectric lamp L, forms a voltage-photoresistance transducer PD,, and thephotoconductive cell R, and the small electric lamp L forms similarly avoltage-photoresistance transducer PD, Accordingly, the resistances ofthe photoconductive cells R5 and R1,, are commonly controlled by theexternal control voltage V A variable resistance R is employed forcompensating discordance between characteristics of the transducers PDand PD Other parts are the same as those of the embodiment shown in FIG.2.

In each of the photoconductive cells R and R is formed by use of CdSwafer, a characteristic curve shown in FIG. 5B is obtained as thecharacteristic of the transducers FD and PD,. In this case, theattenuation ratio of the output voltage E, to the voltage of the inputsignal S, can be changed as shown in FIG. 5A in response to change ofthe voltage across the electric lamps L, and L in this characteristic,the maximum attenuation ratio A is obtained at six volts of the controlvoltage V FIG. 6 shows another embodiment of this invention in which theoutput voltage E, can be controlled by an external control voltage V,and moreover the controlled output voltage E, can be automaticallyregulated to a substantially constant level. In this embodiment, theoutput voltage E is rectified by a rectifier (e.g.; full-wave rectifier12) after amplification by an amplifier 11. The rectified output of thefull-wave rectifier 12 is superposed on the external control voltage Vso as to coincide with the polarity of the external control voltage VAccordingly, this embodiment has an automatic gain control loop. If theoutput voltage E, increases, the attenuation ratio increases also.Therefore, the controlled output voltage E, of the embodiment shown inFIG. 6 can be regulated at a constant level. The time constant of theautomatic gain control loop can be determined at a desired value byinserting, at the output side of the full-wave rectifier 12, a smootherhaving a time constant which corresponds to the desired value.

As mentioned above, the volume controller of this invention can controlan input signal or signal within a wide level range. Moreover, theembodiment shown in FIGS. 4 and 6 can perform automatically suchcontrol. Therefore, the volume controller of this invention is suitablefor use as an element of a fader which is employed to control the levelof each of two seperated but related audiosignals or to controlsimultaneously the levels of combined audiosignals in an audio system,such as broadcast system.

What we claim is:

l. A volume controller for controlling the voltage of at least onesignal transmitted in a signal path, comprising:

a bridge circuit including four resistor arms and having a pair ofopposed input terminals and a pair of opposed output terminals, whereinone of said resistor arms comprises a first variable resistor;

a matching circuit connected between said bridge circuit input terminalsand the output of a signal path;

a difference amplifier having an output terminal, and having a pair ofinput terminals connected to the output terminals of said bridge circuitfor amplifying the difference between signals at said bridge circuitoutput terminals;

a feedback circuit comprising a second variable resistor connectedbetween the amplifier output terminal and one of the amplifier inputterminals;

and control means for simultaneously varying said first and secondvariable resistors; wherein the voltage at the amplifier output can beattenuated over a wide range in response to operation of said controlmeans to vary said first and second variable resistors.

2. A volume controller according to claim I, in which said first andsecond variable resistors are photoconductive cells; and in which thecontrol means comprises two small electric lamps for illuminating therespective photoconductive cells, and a variable voltage sourceconnected to said lamps for vaying the illumination thereof.

. A volume controller according to claim 2, further comprising arectifier connected to said amplifier output terminal and meansconnected between said rectifier and said variable voltage source forsuperposing a rectified amplifier output signal on the voltage of saidvariable voltage source, whereby the controlled output of the differenceamplifier is maintained at a substantially constant level.

1. A volume controller for controlling the voltage of at least onesignal transmitted in a signal path, comprising: a bridge circuitincluding four resistor arms and having a pair of opposed inputterminals and a pair of opposed output terminals, wherein one of saidresistor arms comprises a first variable resistor; a matching circuitconnected between said bridge circuit input terminals and the output ofa signal path; a difference amplifier having an output terminal, andhaving a pair of input terminals connected to the output terminals ofsaid bridge circuit for amplifying the difference between signals atsaid bridge circuit output terminals; a feedback circuit comprising asecond variable resistor connected between the amplifier output terminaland one of the amplifier input terminals; and control means forsimultaneously varying said first and second variable resistors; whereinthe voltage at the amplifier output can be attenuated over a wide rangein response to operation of said control means to vary said first andsecond variable resistors.
 2. A volume controller according to claim 1,in which said first and second variable resistors are photoconductivecells; and in which the control means comprises two small electric lampsfor illuminating the respective photoconductive cells, and a variablevoltage source connected to said lamps for varying the illuminationthereof.
 3. A volume controller according to claim 2, further comprisinga rectifier connected to said amplifier output terminal and meansconnected between said rectifier and said variable voltage source forsuperposing a rectified amplifier output signal on the voltage of saidvariable voltage source, whereby the controlled output of the differenceamplifier is maintained at a substantially constant level.